Magnetic couplings are used to apply rotational torque from an input shaft to an output shaft. Synchronous magnetic couplings typically include opposing sets of magnets disposed on respective rotors rotationally fixed to the input and output shaft. The rotors may be configured in a variety of suitable arrangements, for example comprising concentric disks defining transverse surfaces upon which the magnets are annularly disposed so that the input shaft magnets are separated from the output shaft magnets by an axial gap. In another possible configuration, one of the rotors may define an outer circumferential surface radially separated from an inner circumferential surface of the opposing rotor. The respective magnets are disposed annularly about these circumferential surfaces so that a radial gap is established between them.
Both sets of magnets are arranged so that magnet surfaces are defined at the gap in alternating polarity. If the rotors are turned so that magnet surfaces of the same polarity oppose each other across the gap, the opposing magnets repulse each other. As the rotors are rotated relative to one another, magnets of opposite polarity attract each other, reaching a maximum attraction when opposite poles are directly in line with each other across the gap. If there is no load on either shaft, therefore, the rotors tend to align themselves in this position.
When the input shaft is driven, for example by a motor, the input shaft rotor applies torque to the output shaft rotor through the magnetic interaction between the opposing magnets. Generally, a first magnet pole on one rotor is aligned between two opposite polarity second poles on the other rotor across the gap. Thus, assuming that the two second magnet poles are on the driving rotor and that the first magnet is on the driven rotor, torque is applied through the attraction and repulsion of the two second magnet poles to the first magnet pole, and the output shaft rotates synchronously. The rotors maintain synchronous rotation until the output shaft's load overcomes the magnetic torque applied between the magnets. At this point, the output rotor begins to slip with respect to the input rotor.
An asynchronous coupling generally includes only one set of magnets (arranged in alternating polarity), for example disposed on the input shaft rotor. An electric conductor is disposed on the output shaft rotor so that the conductor opposes the input rotor magnets across the gap so that magnetic flux of the magnets passes through the conductor. The conductor may comprise an annular ring made of a material such as copper or aluminum and that is concentric with the output shaft. When the input shaft is rotationally driven, the changing magnetic field induces an electric current in the ring, thereby generating magnetic drag that causes the output rotor to rotate with the input shaft, but at a lower speed.
Since the output shaft of the asynchronous coupling slips with respect to the input shaft, it is less efficient than the synchronous coupling. On the other hand, it provides a more gradual, or "softer," start to the output shaft. As should be understood by those skilled in this art, synchronous or asynchronous couplings may be more appropriate in a given system.